It is proposed to carry out several experiments using the low-angle X-ray diffraction camera developed for the Stanford Synchrotron Radiation Project (SSRP) by N. G. Webb, S. O. Samson, R. M. Stroud, R. C. Gamble, and J. D. Baldeschwieler with the support of the National Science Foundation under Grant No. MPS73-08815. The synchrotron radiation source and the novel camera are expected to shorten X-ray exposure times by two orders of magnitude in comparison with a conventional camera. It is proposed to study rhodopsin-containing membranes to look for changes in the structures of the membranes after bleaching. Both detached visual-cell outer segments and artificial membranes, containing rhodopsin, will be studied. The rod outer segments specimen has the advantage that it can be prepared quickly, and the rods can be oriented in a magnetic field. The artificial-membrane preparations may have the advantage that there will be less disorder, assuming that the membranes can be stacked more closely together than in the rod. A method for orienting the vesicle membranes in these preparations has been described by others. Specimens will be exposed on a conventional low-angle X-ray camera, as well as on the diffraction camera especially develped to use the synchrotron radiation generated at the Stanford electron storage ring. This intense source, and the proportional counter now being perfected, will enable shorter exposures than ever before, to look for early changes in membrane structure following exposure to light. An experiment on myelinated nerve is also proposed, in the hope of obtaining a pattern showing less of the effects of stacking disorder than has been found in the long, conventional exposures up to now.